All cultures have procedures for accessing ASC but differ in their attitudes toward these states and the means for controlled access (Laughlin et al., 1992). These universals of shamanistic practices reflect underlying brain structures and functions that elicit operations of an integrative mode of consciousness (Winkelman, 2000). This integrative mode of consciousness reflects the ubiquitous response of the brain to diverse conditions that induce synchronized limbic system discharge patterns. These discharges entrain across the neuraxis of the brain, synchronizing the frontal cortex with coherent slow wave EEG patterns in the alpha and theta range (Mandell, 1980; Winkelman, 1986b, 1992, 2000). Physiological mechanisms underlying the integrative mode of consciousness are based in neurobiochemical pathways involving activation of the temporal lobe and limbic system serotonergic pathways to the lower brain (Mandell, 1980). These lim-bic system processes integrate information from the whole organism into emotion and memory, and mediate self-preservation, family behavior, novel sensory information, and control of the sleeping/waking cycles.
ASC of other shamanistic healers may involve soul journey, but typically have other psychophysiological and experiential dynamics. Possession ASC of mediums have characteristics of a "take over" of the person by spirits (Bourguignon, 1976; cf. Goodman, 1988; Lewis, 1988) and temporal lobe symptomology (tremors, seizures, convulsions, and amnesia) (Winkelman, 1986b, 1992). Possession is not a unitary phenomenon, but involves a variety of different psychodynamic processes including dissociation, illness, communication, role enactment, and political struggle (Boddy, 1994; Shekar, 1989). Possession ASCs predominantly occur in complex societies with hierarchical political integration and reflect the psychody-namics of oppression and powerlessness (Bourguignon, 1976; Winkelman, 1986b, 1992). Meditative ASC are characterized by deliberate relaxation (direct parasympa-thetic activation) and focus of attention. Castillo (1991) characterizes meditative practices as involving the differentiation of a participating self engaged in the world from a detached observing self. The neuroendocrine mechanisms of meditative effects on physiology and psychology involve stress reduction through enhancement of serotonin functioning (Walton & Levitsky, 1994) and stimulation of theta brain-wave production. Meditation intervenes in the stress cycle, inducing relaxation, lowering autonomic arousal, and enhancing brain-wave coherence in theta frequencies. Meditation increases serotonin levels, reducing cortisol levels and the limbic system's anger and fear reactions. This mirrors Mandell's (1980) serotonergic model of ASC and suggests serotonin's generic role in the therapeutic mechanisms of ASC, manifested in synchro nous high-voltage, slow frequency brain-waves (alpha, theta, and delta activity, especially 3-6 cycles/s).
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